Conventionally, a technique to adjust a threshold for voice recognition and so on in accordance with a usage (operating) environment of a voice recognition device is proposed. For example, in Patent Document 1, the following voice recognition device is proposed: it is determined whether a vehicle is under a quiet environment or under a noisy environment by comparing a current speed of a vehicle with a reference value, a threshold (detection level) for detecting a section of voice activity under the quiet environment and under the noisy environment based on the said determination result is changed, and the threshold in a case under the noisy environment is set to be higher than that under the quiet environment, which solves an inconvenience such that an erroneous detection of the section of voice activity is rendered due to a sensitive reaction to a minute sound, a level fluctuation in the residual components of an audio sound, or the like.